1. Field of the Invention
The present invention relates to a method for detecting an arc and protecting a load against the arc. Particularly the present invention relates to an electrical component in an automotive vehicle, which, through an electronic system, analyzes samples of current circulating through a load and disconnects said load from the feed when an arc is detected.
2. Description of the Related Art
Patent document WO-A-02/39561 teaches an apparatus providing detection and/or protection of an electric system against parallel arcs and series arcs. In this reference, different detection parameters are provided. Different apparatus having different configurations depending on the variable to be monitored and on which the detection of parallel and series arcs will be based. In some cases the voltage in the load, in other cases the intensity circulating through the load, and in yet others the intensity in the load and the voltage in the source will be monitored. On the basis of the values obtained by this monitoring, those values are compared with pre-established thresholds for rated voltage and rated intensity in the load. When these monitored values exceed or fall under said thresholds, depending on if it is voltage or intensity, and are maintained for a certain time in those exceeded or fallen ranges, it will be indicated that a parallel or series arc, has been detected, and the load will be disconnected from the feed and/or series of alarm signals will be activated, such as, for example, LEDs being lit.
The biggest drawback of this apparatus is that the predetermined time, during which it is observed if the monitored values are maintained above or below the pre-established thresholds, is very high, a minimum of 10 ms. but preferably 20 ms., being taught. During this time period there is no protective action against an arc being carried out, which is very dangerous for the load, because before the load is disconnected from the feed, it could have be seriously damaged for having maintained the arc too long. Another drawback of the apparatus is that the instantaneous value of the intensity or voltage in the load is compared continuously, which can make certain transient phenomena falsely effect the result of said comparison.
U.S. Pat. No. 5,933,305 issued Aug. 3, 1999 to Schmalz et al teaches the possibility of carrying out arc detection by the analysis of values acquired by a monitoring component, during a certain interval, comparing the result of said analysis with other previous ones and expressing the result of said comparison in the form of bits (1 when an increase occurs with regard to a previous interval, and 0 when this comparison provides a negative result). Said bits are stored in a shift register and are therefore updated every certain number of bits, depending on the capacity of the register, and if they are representative of a sufficient number of changes indicate that an arc has occurred (this number is marked by a counter), it acts accordingly, disconnecting the load from the feed. As this method does not take into account the amplitude of the samples, it can be used to detect parallel arcs as well as series arcs. The fact that the amplitude is not taken into account is also a drawback, since the types of arc are not differentiated, nor is the detection of a possible short circuit taken into account which would make the immediate disconnection of the load from the feed essential, without waiting for a larger number of samples to be analyzed. This slowness in the response to an arc on the load could cause potentially irreversible damage to the electric system.
U.S. Pat. No. 6,388,849 issued May 14, 2002 to Rae teaches an arc detector and a circuit responsible for disconnecting the feed from the load in the case of an arc. The teaching is directed to the case in which the arcs occur in an alternating current (AC) electric system. The method used by said detector to generate an arc signal and therefore make said disconnecting circuit act is based on carrying out a moving average, taking the period of the frequency of said alternating current as a reference, with acquired instantaneous current values and if the value obtained exceeds a preset threshold, an arc signal is generated. To prevent false detections due to other transient phenomena which also modify the average current value, another method is disclosed which also includes a pulse generator that will ignore said transient phenomena and will generate pulses every time it detects a step increase in current. Said generator can even act as a function of a predetermined value of pulses generated every time an arc occurs. In the case where said pulse generator is included, the arc indicating signal will be determined by the average current value obtained exceeding the preset threshold and whether the pulse generator generates a pulse, i.e. both situations must occur for an arc signal to be generated and for the detector circuit to act accordingly. Said document does not mention the possibility of being applied in a direct current (DC) electric system. It is also clear from the document that, as in the previously mentioned references, the action against a possible arc is not very fast, since the analyses are carried out in half-periods or periods of the frequency of the alternating current. Nor does it indicate if the proposed detector serves to detect series and parallel arcs, and if it is capable of differentiating them, since it only refers to acting in case the average current value excessively exceeds a preset threshold. This reference also values from which the threshold is compared with the calculated average current value, indicating that the latter has one or several set values.
It is therefore still desirable to provide greater reliability when detecting series and parallel arcs, as well as short circuits and, especially, a faster detection, which will be reflected in an almost immediate action on the load if one of said phenomena occurs by disconnecting the load from the feed.